1. Field of the Invention
The invention relates to a heating element comprising a layer forming an electrical resistance which is situated between two planar electrodes extending approximately parallel to each other and to the said layer and, suitably but not exclusively, comprising an insulating layer situated on the side of the electrode facing away from the said layer, in which the flow of current occurs at right angles to a plane which extends approximately parallel to the layer forming the resistance, and to a method of manufacture thereof.
2. Description of the Prior Art
Planar heating elements devised by the present inventor are already known, which comprise an electrical layer resistance between material of satisfactory electrical and thermal conductivity, with the flow of current occurring substantially at right angles to the plane of the layer. The electrical layer resistance is then formed by electrical resistance compositions which, for example, consist of silicone rubber with electrically conductive and semiconductive particles homogenously distributed therein, or of an electrically conductive composite material, in which the synthetic resins are mixed with metal compounds in a quantity such that approximately one metal or metalloid atom is provided per molecule of synthetic resin, from which the ions are eluted and the dispersions, solutions or granulates obtained in this manner are mixed with graphite or carbon black for further processing. The electrodes situated at either side of the electrical layer resistance are covered with insulating materials if required, to prevent contact with conductive parts. The phenomenon, which is also utilised by the inventor in the present application, was described in Austrian patent specifications Nos. 325 176, 274 965 and 313 588 amongst others. Such planar heating elements proved satisfactory in practice under application of different resistive compositions.